This project investigates the significance of immunologic factors in periodontal disease. Indicators of general immune capacity and specific immune response to antigens common to dental plaque will be compared between persons with severe periodontitis and those with a healthy periodontium. All subjects will be free of systemic disease as determined by a thorough medical evaluation. Their periodontal status will be characterized fully, using standard indices and a total attachment loss index. Their general immunologic status will be evaluated by assessing serum immunoglobulins and complement components with radial immuno-diffusion, blastogenesis of peripheral lymphocytes stimulated by mitogens, levels of T- and B-lymphocytes by rosette formation, capacity to mount dermal hypersensitivity (Type IV) response, and phagocytic capacity of polymorphonuclear leukocytes. Specific immunity will be assessed by serum antibody levels, blastogenesis and lymphokine synthesis by lymphocytes and dermal hypersensitivity related to antigens derived from dental plaque organisms. Difference in any of the immune measures between experimental and control subjects will be sought and pursued when found.